First Integration Steps of Cu-based DNA Nanowires for interconnections

In the wide range of emergent nanotechnologies, DNA-based microelectronics has shown an important potential for components miniaturization and auto-assembling approaches applicable to future silicon-based electronic circuits [1]. In order to pursue the Moore's law, interconnections must be indeed addressed at the nanoscale, with a good control of their size, location and electrical & thermal performances. With its natural auto-assembling property, its 2-nm-double-helix diameter and its several metallization possibilities, DNA is a promising candidate to build bio-inspired electronic components [1]. DNA has been first metallized by Erez Braun in 1998 using a silver electroless method [2]. Since 1998, several groups have worked on DNA metallization using different chemistries with metals such as Pd, Pt, Au, Ag and Cu [3]. Most of these works have presented electrical and morphological characterizations of few metallic nanowires. However, in order to initiate DNA-based-nanowires integration on silicon technologies, we must start to implement nanowires on silicon at wafer scale. We have thus developed a platform based on silicon technologies providing morphological and electrical characterizations of copper nanowires built from DNA [4]. This platform will allow us to simultaneously characterize a large number of nanowires, returning a statistic of their electrical performance, and thus allowing the optimization of the copper nanowire metallization process. Two main approaches are proposed to fabricate and contact a large number of copper nanowires with metallic electrodes in order to study their electrical behavior. In both approaches, a linear 16-μm-length DNA phage is used. The first approach consists in aligning DNA wires on a hydrophobic silicon oxide surface by a method called DNA combing. On a second time, aligned DNA wires are all metallized by electroless process [4]. 5-nm-diameter copper nanowires have been so far achieved by this method and focus on improving the metallization process is currently at stake. Finally, Ti/Au electrodes are fabricated on the nanowires by a classical lift-off process in order to electrically connect them. The advantage of this approach is the very accurate nanowires alignment and their homogeneity over the surface. However, the low number of aligned nanowires per surface unit (10–20μm−2) and the high electrical resistance of each (>kohms) makes the electrical characterization quite complex. On the other side, the second approach consists in fabricating the Ti/Au electrodes first and then aligning or randomly depositing the copper nanowires at their surface. Same protocols are used to align and metallize the DNA nanowires for both approaches. The advantage of this second approach is a higher nanowire density deposited on the electrodes. However, a higher contact resistance and a lower control of nanowires alignment are obtained. Both approaches are currently explored and permit to explore a wide range of parameters for copper nanowires metallization process improvement.